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Author: Subject: PTFE joint sleeves
UnintentionalChaos
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[*] posted on 1-6-2009 at 12:24
PTFE joint sleeves


So, I have the option of purchasing some VWR teflon joint sleeves (http://www.vwrsp.com/catalog/product/index.cgi?catalog_numbe...) for my ground glass distillation setup, although the cost is around $4.50/ea. For those who have used them before, are they worth this much and how many uses can I expect to get out of them? Is there an average lifetime, or will they last more or less forever if I take care of them? Thanks for the help.

I also see that this site: http://www.sciencegear.com/prices-labware.htm#sleeves has them for a lot less ($1.50/ea). Ignoring the $50 min. order, do you suspect that those are lower quality or is it simply offbrand that makes them so cheap?




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DJF90
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[*] posted on 1-6-2009 at 14:07


The second lot are disposable ones, they are much thinner. The product just below ($10+ each) are reusable.
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entropy51
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[*] posted on 1-6-2009 at 16:36


Unintentional Chaos,

I know it goes against the conventional wisdom here abouts, but I've tried the PTFE sleeves many times and I keep returning to silicone vacuum grease. I don't think the sleeves seal that well for water aspirator vacuum, although they do better with mechanical pump vacuum. I don't trust them at all to seal tightly when distilling bromine or ether.

My experience with standard taper joints is:

1. You don't need grease or sleeves unless the joint will be exposed to vacuum, strong alkali, or temperatures above 100 C. Concentrated inorganic salt solutions also probably need grease on the joints if the material enters the joint. I use grease for particularly nasty or flammable materials like bromine and ether.

2. Use a thin layer of grease. I use a robust toothpick to spread a thin layer uniformly around the male joint.

3. Disassemble the joints soon after finishing the experiment, or at least give the joint a turn after it cools.

4. A thin layer of grease can be removed with a paper towel, or if you use too much, immersion in a base bath of 10% KOH in ethanol over night.

I haven't had a joint freeze on me in a very long time, and I've never had one freeze so badly that a quick pass with a heat gun (kept in constant motion around the joint) wouldn't free it up.
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UnintentionalChaos
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[*] posted on 1-6-2009 at 22:24


Hrm. How about Glindemann sealing rings? They are rather pricey and don't seem terribly reusable though, but they claim they get a much better seal than sleeves.



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BromicAcid
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[*] posted on 2-6-2009 at 04:24


You can reuse Glindemann rings. You get a bunch of them for one price. To get the best seals you have to use two of them.



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Crucible
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[*] posted on 14-6-2009 at 15:49
teflon tape


How about wrapping joints in teflon tape? Will the hardware store variety work? I've heard if you do it wrong it can put stress on the joint and maybe crack it. What is the proper way to wrap teflon tape around a joint?
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Panache
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[*] posted on 14-6-2009 at 16:09


Quote: Originally posted by Crucible  
How about wrapping joints in teflon tape? Will the hardware store variety work? I've heard if you do it wrong it can put stress on the joint and maybe crack it. What is the proper way to wrap teflon tape around a joint?


Go to a plumbing specialist supplier and get them to order in 1" wide gas sealing teflon tape. This is high density TFPE, by standard, not the low density PTFE used for water pipe. The extra width means you need few overlaps and hence this lessens the stress issues inherent with using tape. I have not assessed this conclusion just supposed it.

Once practised you require no overlaps and the seal is tres super fantastic. I assessed the leakage rate on my dessicator and i have held a solid vacuum for weeks using the tape. Silicon grease works better at STP but not for heat cycling conditions IMO. Buy some cheap hairdressing scissors (i got mine free with an electric beard trimmer), they cut the tape straight and clean.





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Crucible
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[*] posted on 16-6-2009 at 18:17


Quote: Originally posted by Panache  

Go to a plumbing specialist supplier and get them to order in 1" wide gas sealing teflon tape. This is high density TFPE, by standard, not the low density PTFE used for water pipe. The extra width means you need few overlaps and hence this lessens the stress issues inherent with using tape. I have not assessed this conclusion just supposed it.


Wow, finding that tape was a quest. They don't carry the yellow gas tape in 1" widths in this area is what I've found. I got the Blue Monster tape instead. It is supposed to be almost as dense as the gas tape. Hopefully it will do the trick. And I don't know who you are getting to make small quantity special orders, but none of the plumbing supply shops I talked to were willing to do it without a huge surcharge.
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jimwig
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[*] posted on 17-6-2009 at 08:12


ebay ebay ebay

http://www.rmiorder.com/index.php?link=browse&code=Z-TT-...

ebay got me there

[Edited on 17-6-2009 by jimwig]




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[*] posted on 17-6-2009 at 17:18


Quote: Originally posted by jimwig  
ebay ebay ebay

http://www.rmiorder.com/index.php?link=browse&code=Z-TT-...

ebay got me there

[Edited on 17-6-2009 by jimwig]


Hmmm, they have some interesting stuff on there, but what they don't have is yellow gas sealing teflon tape. They have the regular white tape and the green oxygen tape. Teflon tape comes in many colors, which correspond to various densities (and probably other things as well).

Ebay does have an amazing variety of teflon tape. For some reason ebay isn't the first place I think to look for hardware store type things like tape, but there it is. I didn't see any yellow gas tape in 1" width, but that could well change. At any rate I think the blue tape will do. Now I just need to figure out how to wrap it completely, yet without overlaps as Panache suggested.
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itchyfruit
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[*] posted on 24-6-2009 at 09:42


saw these on Ebay uk item no :- 110394981487
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chemrox
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[*] posted on 24-6-2009 at 20:37


try Scientific Machine and Supply in Middlesex, NJ. Ask for Elizabeth or write to info@scimac.com. They developed the process for making these sleeves and sell them to the other vendors discussed above. They can help replace stopcocks as well.



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